1. Field of the Invention
This invention relates generally to prosthetic feet.
2. Prior Art
A footstep is comprised of a downward portion when the heel touches the ground, a rocking portion when the foot rocks from back to front on the ground, and a upward portion when the toes lift off the ground. A prosthetic foot mimics the way a real foot absorbs energy on the downward portion of the step to soften the impact, and returns the energy on the upward portion of the step to help the user move forward. These effects are typically achieved by using elastic polymer materials, particularly in the heel and toe portions, to provide longitudinal flexion. However, some prosthetic feet require precision metal components that raise the cost of the feet. The metal parts also tend to wear out and separate from the surrounding plastic parts after a relatively short time. Most importantly, many prosthetic feet lack torsional compliance, that is, they cannot twist about a longitudinal axis. Although they perform well on flat and level surfaces, they lack the necessary torsional compliance when the user steps on an uneven surface, or when the user takes a step with the leg off to a side, such as when playing sports, dancing, etc.
My prior U.S. Pat. No. 5,376,240 discloses a prosthetic foot that provides the important torsional compliance. It is comprised of a internal frame embedded in a foam foot-shaped outer body. The frame is embedded with loose carbon fiber strands for improved strength and elasticity. The frame is in the shape of a modified trapezoid, wherein the back member is generally vertical and the front member is substantially oblique. The lower end of the front member is disconnected from the bottom member, and a bearing is provided at the interface there between. The bearing is comprised of a truncated cone at one mating surface, and a socket at the other mating surface.
The bearing enables the toe part of the foot to twist about the longitudinal axis for compliance on uneven surfaces and when the leg is at an oblique side angle to the ground. However, the loose carbon fiber strands do not provide sufficient strength or elasticity. The rounded heel is not compliant enough to absorb much energy. A short toe member at the front end of the frame terminates before the toe portion of the outer body, so that it does not support the weaker foam toes during the rocking portion of the step. The foam toes do not return much energy, and tend to break very quickly from the repeated bending. Most importantly, the truncated cone separates from the socket when the foot kicks an obstacle, such as a curb, and the foam outer body may tear and cause the user to fall.
The objects of the present prosthetic foot are:
to have heel and toe portions flex longitudinally on the downward, rocking, and upward portions of a step;
to absorb more energy on the downward portion of the step;
to return more energy on the upward portion of the step;
to be stronger and more elastic;
to have a toe portion with torsional compliance for situations other than walking on a flat surface;
to resist breaking when kicking an obstacle; and
to be inexpensive and durable.
Further objects of the present invention will become apparent from a consideration of the drawings and ensuing description.
A prosthetic foot is comprised of a springy internal frame embedded in a resilient foot-shaped outer body. The frame is in the shape of a modified trapezoid, wherein the shorter top member and the longer bottom member are connected by a generally vertical back member, and a substantially oblique front member. A toe member extends from the bottom member into a toe portion of the outer body. A solid carbon fiber layer is embedded in the frame for strength and elasticity. A break is provided between the lower end of the front member and the bottom member to enable the toe portion of the foot to twist about a longitudinal axis. A flexible cord is connected across the break to prevent the front and bottom portions of the frame from separating when the foot kicks an obstacle.